Double Planking Construction-Questions

[RodB]

When building in traditional methods it seems theres very little information on the double planking method of construction (for say 28-32 foot sailboats). The fist layer would be say 3/8" thick cedar, while the outside layer of say mahogany would be greater than 1/2". I have read the little blurp available in Stewards "Boatbuilding Manual" but have found little more.

What are the pros and con's of this method? Since it would result in a stiffer and stronger hull than plank on frame would the extra work be worthwhile? Would this be considered an intermediate method between traditional carvel planking and strip-planking. I'm assuming maintenance woud be very similar to traditional carvel planking.

I will be using the boat I build in a very warm climate, and have always thought an epoxy encapsulation building method was best for longevity in these conditions (sheath-striped and /or cold molded). I hadn't really considered traditional construction but with the advantages of not using epoxy (cost and mess) I want to at least consider it.

It would seem that a boat built traditionally (double planked or plank on frame) could stand up to the warm enviornments with proper wood selection (non-rotting species) and construction that allowed for good ventilation.

I would be interested in any feedback on the double planking construction method and traditional wooden boats maintenance problems in real warm enviornments.

RB

[Tonyr]

Is the second layer put on in the same direction as the first, or at an angle?

Thanks, Tony.

[Nicholas Carey]

Originally posted by rodbrink:
When building in traditional methods it seems theres very little information on the double planking method of construction (for say 28-32 foot sailboats). The fist layer would be say 3/8" thick cedar, while the outside layer of say mahogany would be greater than 1/2"...What are the pros and con's of this method?It depends on what flavor of double planking you're talking about. It can be</font> double-diagonal planking.
The inner layer of planking runs at a 45 degree bias to the centerline of the boat. The outer layer is conventionally planked fore-and-aft.
</font> fore-and-aft (for lack of a better term).
The inner layer of planking is laid conventionally, running fore-and-aft. Ditto for the outer layer, except the the plank edges are offset by 1/2 plank.
</font>In both types, the layers of planking are separated by a layer of gasket and 'goo' (for some definition of 'goo'). Traditionally, a layer of calico and white lead paste:</font> inner planking</font> white lead paste</font> calico</font> white lead paste</font> outer planking
</font>These days, I believe (at least in the mahogany speedboat world,) it's trendy to use dynel and some miracle goo (5200, epoxy, polysulfide, etc.) in lieu of calico and white lead paste.

Typically, I believe the inner planking has no caulking bevel nor is it caulked. It's tacked in place with thin nails&mdash;The screws or rivets fastening the outer planking wind up holding everything together. The outer planking, of course, has a conventional caulking bevel and is caulked in the usual manner. Finally, double planking is back-screwed from the inside: small round-head screws with washers are installed between frames to tie the inner and outer layers together.

The first type (double-diagonal) makes a markedly more rigid hull as it has a lot of resistance to racking forces. Its big drawback, obviously, is that repairing/replacing any inner plank theoretically requires removing every outer plank on that side of the hull, assuming the planking job was properly done. That's a lot of fasteners to remove :eek:

OTOH, I believe that double planking makes for a tighter, stiffer hull (Pirate is fore-and-aft double-planked, western red cedar inner planking and teak outer planking: she didn't leak a drop&mdash;not one&mdash;when we splashed her after three years on the hard. Not bad for 80 year old planking.)

I think double planking can give you a lighter and possibly cheaper (in terms of cost of materials&mdash;bear in mind that with the backscrews we're close to doubling the number of fasteners) than a single planked hull.


Since it would result in a stiffer and stronger hull than plank on frame would the extra work be worthwhile?Only you can answer that question, I think.


Would this be considered an intermediate method between traditional carvel planking and strip-planking. I'm assuming maintenance woud be very similar to traditional carvel planking.I'd say it's more transitional to cold-molded, but the maintenance should be about exactly similar to conventional single planking...and I don't believe that a double planked hull would be much happier than a single-planked carvel hull on a trailer. It wants to be in the water.

And it won't reduce the framing schedule, either. You're going to have the same number of frames as you would if it were single planked.


...I hadn't really considered traditional construction but with the advantages of not using epoxy (cost and mess) I want to at least consider it.Bronze screws or copper boat nails and roves cost money, too. And the goo between the planking layers is at least as messy as epoxy. 5200 and polysulfides are kind of like cholla cactus (http://www.desertusa.com/mag99/may/papr/chollas.html), in that they, like cholla (http://www.google.com/search?q=cholla+cactus) seemingly jump on you and anything nearby.


It would seem that a boat built traditionally (double planked or plank on frame) could stand up to the warm enviornments with proper wood selection (non-rotting species) and construction that allowed for good ventilation.I think proper maintenance counts at least as much toward a wooden boat's longevity as will the choice of wood used (assuming you use a good boat wood). Certainly construction choices play a part, especially painting/sealing all faying surfaces and the like, sealing the frame ends and keeping water out of the boat. I think a good plywood, dynel and glass deck and housetop will go further towards keeping the boat alive for a long time than will you choice of woods.

That means keeping the vessel ventilated (and covered if you want to preserve your brightwork: UV kills.), keeping standing water out of the bilges, annual haulouts and doing any maintenance that needs doing when it needs doing&mdash;touching up/repairing paint and varnish when it gets damaged, etc.

Deferred maintenance on a 'glass boat results in a ratty looking glass boat; deferred maintenance on a wooden boat results in a rotten boat and a whole lot of work.

&mdash;
Download Complete :D

[Wiley Baggins]

Paul Gartside (and others?) have added a twist similar to the 3M 5200 method referenced above in that he glues the layers with epoxy. More information at gartsideboats.com. (http://www.gartsideboats.com/22steam.php)

[RodB]

Thanks for all the detailed feedback.

I'm definitely talking about the fore and aft planking with the outer layer offset by 1/2 plank.

Steward begins,"The purpose of double planking is twofold: it insures watertightness without periodic recaulking, and a sleek finish that is relatively easy to maintain... The total thickness of planking is the same as single planking, but weight can be saved over a single -planked mahogany job by planking the inner layer with a good, lightweight wood such as Alaska, white, or Port Orford cedar. ..Before each outer strake is fastened, it is first coated on the inside with a double planking compound, such as one made by Dolphin. An alternative treatment once used by two of the best practitioners of this planking method
-- Nevis and Herreshoff-- is a thick coating of shellac between the inner and outer layers of planking. All seams are fitted tightly together without out-gauge, as no caulking is necessary," etc., etc., etc.

He continues, "The whole job is very strong because the two layers are so completely tied together".

He goes on to describe the method of fastening the inner and outer strakes to each other. He also says ,"The garboard plank is usually made single layer so that it can be readily replaced if necessary; it is easier to plane a proper caulking seam on a single edge".

The "no caulking necessary" is quite attractive plus the ease of a sleek finish. I'm wondering how the interior wood would be treated, ie., a deep penetrating oil or varnishing, or nothing?
I'm assuming the bilge would be painted with red lead but what about the interior surface of the hull? What about the outside of the hull, just primer and anti-fouling paint?

When you've worked in epoxy (stitch and glue construction) you can't help but be a little uncomfortable when considering bare wood and no epoxy around!? I obviously know nothing about traditional boatbuilding.

This method appeals to me for several reasons, I' m wondering how cost would compare between this method and strip-planked construction (sheath-stripped)?

It definitely sounds easier to plank the hull with the thinner material compared to standard thickness carvell planking. Since this boat will be in the water most of the year I want to be aware of all my options.

RB

"

[imported_Conrad]

Go with the strip planking/sheathing. The thinner planks can be tough to lay fair, there will be gouge involved anyway, you'll get really tired of driving expensive screws, and the hull won't be significantly stronger than single plank. If you've never built a boat before, and are likely to be working a lot by yourself, strip is a great way to go. Done traditionally, double longitudinal planking can lead to rot. Done the "modern" way it's a lot of work with no significant advantages, and either way it's hell to repair.

[ 07-18-2003, 04:07 PM: Message edited by: Conrad S. ]

[rbgarr]

I worked briefly at Seth Persson's shop when he was building his last double-planked cruising sailboat, SANKATY III, a Sparkman and Stephens 32' sloop. He also built FINISTERRE, an S&S design, and ROGUE, a Herreshoff design, both a bit larger, and also longitudinally double-planked.

The SANKATY III (now AURA II, I believe) was built in the fashion described by Steward (close-fit, 'uncaulked' outer planks) but it is work that demands a high level of spiling and fitting skill to get right. Scheduling the placement of buttblocks is a bit tricky, and should be carefully planned. In her case, the fastenings from inner to outer planking were wood screws and outer planking through to frames, rivets, if I remember correctly.

Depending on the shape of the hull you choose (RB) there may also be double the amount of 'backing out' to do (planing a concave surface on the inner face of the planks where they meet inner planking or framing). Fitting any muslin/calico/dynel (in whatever liquid medium) is a skill in itself and care needs to be taken to avoid folds, 'wraps' (or bunching when drilling and fastening) and keeping a clean surface for fitting the outer plank... while doing much of this work overhead. My understanding is that rot often starts in those areas, much like problems arise with voids in plywood, fiberglass or epoxy encapsulated boats. I'd go with a non-adhesive bedding compound after trial fitting the outer planks, myself. Setting londitudinal double planks in epoxy or 5200 would be a repairer's nightmare, IMO.

I see AURA II from time to time and she looks as smooth as the day she was launched 28 years ago. I love the look of a well done double planked hull, but unless I KNEW it was built by real craftsmen and maintained well, I'd hesitate to own one. A surveyor will have a difficult time telling if there are incipient problems in those many interior surfaces, I think, and the skills, tools, and materials needed to repair problems properly exceeds those needed to build it in the first place, if they are even available (locally, that is).

In my opinion, this choice of planking style was well suited to a production method like that developed at Herreshoff's. They had highly skilled and coordinated craftsmen, building with top notch materials with an eye toward minimizing waste, working 'down' on a hull that would be rolled over for finishing. The boats were built for minimum effective weight and were maintained meticulously by wealthier owners, often strictly for racing, and sometimes afloat year 'round. See back issues of WB or Bray and Pinheiros book 'Herreshoff' (also from our sponsors) for pictures of this method of construction and the results.

None of this is meant to discourage you. If you're up to it, and enjoy the challenge, go for it. It would be a deeply rewarding AOL (Achievement of A Lifetime) to have a well-built design that you loved, knew every inch of, enjoyed building, maintaining and sailing.

[ 07-18-2003, 06:58 AM: Message edited by: rbgarr ]

[RodB]

Well, it is a little discouraging especially when your going to be learning so may new skills. It seems that strip-planking is by far the easiest method for the first timer. The double planking method seemed not that difficult when reading a synopsis of the procedure but in reality it sure has its technical difficulties.

My only dislike of strip-planking is the need to add a couple of layers of veneer to the outside to get a really stable hull, at least that seems to be the most common feedback I get. The other alternative is to glass the exterior heavily in lieu of not adding layers of veneer, plus the interior would have to be glassed according to the scantling rules.

The double planking method at first glance seemed to offer some advantages without too much difficulty. When you live in a hot enviornment the idea of plain old cold molding seems the most promising for longevity of all methods. I can only afford to do this once, so I will need to make a well informed and wise decision.

There doesn't seem to be a straight forward answer, too may factors to make the decision simple.

RB

[imported_Conrad]

Boats were built for many years with only the strip planks, no extra wood or glass added inside or out. Make your strips a bit thicker if you feel the need for extra stiffness/strength, and only put a layer of light glass (6-10oz.) on the exterior to improve the finish. Many strip boats were built with nothing, or only paint, between the strips, not even glued, but plenty of nails or dowels in a regular pattern down through two or more strips. They don't move, they'll hold an almost perfect finish if properly primed, and since there's no space or voids between planks to trap moisture the almost never rot from the bottom up. But, like any boat, they'll rot from the top down if rain gets in through the deck fittings, etc.

Search the Wooden Boat index for an article about The Pulsifer Hampton built in Maine by Richard Pulsifer (also a current advertiser- look in a current issue). It's strip, traditional without glass, etc, and seems to last forever. ;)

[brian.cunningham]

Cold molded boats are the next evolution from double and triple planking.

I'd look into that as well.

[john welsford]

New Zealand still builds a lot of woodden boats, and since way back ( see John Bs posts about Logan Boats) has favoured double diagonal construction for lightweight boats. I had the privelege of helping on a major repair to the Logan built "Thelma" now past her centenary and can verify that the two copper riveted layers of wood had a thin layer of high grade felt in white lead and linseed between them.
But during the late 50s waterproof glues became available and literally thousands of mid sized yachts were built with the two layers solidly glued together with Phenolic or Urea formaldehyde resin glues. The boats were typically painted inside ( some people seem to forget that boats were built before epoxy was thought of, and that it is possible for a boat to last more than a mans natural days without slathering the thing with poisonous plastic inside and out) and sometimes given a covering of 6oz glass.
Most boats were two layers over stringers, the layers seldom more than 6mm, a bigger boat got more layers otherwise the angled planks moved and printed through the paint.
Boats with three or more layers often had only one or two stringers plus the carline, and a few floors. This can, with an organised builder be a pretty quick way of building, does not require great baulks of high grade lumber as the individual peices are small and slight defects will be reinforced by the layer to cover it and the big knots and such can be cut out. Pieces are light and easy to handle, fastenings may be permanent or temporary , and yes the planks are typically at 90 deg to one another.
Makes a nice hull, stiff and strong and dry.
For skantlings there are a number of publications which would help, the one that I use is "Cold Moulded and strip-planked wood boatbuilding" By Ian Nicholson, pub Stanford Maritime London ( the London in England) ISBN 0 540 07147 1 .
His suggestions tend to build a slightly heavy boat by my standards, but its a very good start.

JohnW

[Lion]

Rod

Interesting question and great responses. If you look at www.gartsideboats.com (http://www.gartsideboats.com) you will see how 'Surprise', which was featured in our sponsors mag no 172, was built using this method. I think the sealing between the inner and outer was done with epoxy. Interestingly Paul Gartside has redrawn her as 'Surprise II' , which although beamier, the primary difference seems to be that it is 'cold moulded' with a diagonal intermediate layer and finished with a fore & aft layer.
Look at his site and give him a call, he has done it both ways. Better still, use one of his very handsome and salty designs.

Lion

[RodB]

Lion,

I have recently e-mailed Mr. Gartside back and forth exactly on this subject . He recommends the double planking with the first layer being diagonal, and the outside layer fore and aft. He also commented on the skill level required to do it right.

I'm not convinced that is the way I would go; am leaning more towards more modern methods, ie cold molding or strip-planked/cold molded.

RB

[Ken Hall]

Another question: In The Riddle of the Sands, yawl Dulcibella was a converted lifeboat built of double-diagonal teak.

I've been intrigued with that method and material ever since I read the book. D'you reckon that you'd have to steam the inner planking to force it to shape? I'm not familiar with the bending properties of teak, but I like everything else about it.

[Aramas]

Of course Dulcibella has the advantage of being fictional, but my guess is yes, they would have been steamed.
At about that time Albert Strange wrote a bit about the building of Cherub II and mentioned having to steam the 1/4" mahogany diagonal planks.
Just about any wood will steam bend to a certain extent, it's just that some are better suited to it than others. It is just a fibrous polymer, after all.
And of course there's teak, and there's teak. The stuff you buy now is almost certainly not from India or Burma, as it was in the days of empire. Even if you can get your head around rampant corruption, trashing rainforest remnants and the forcible relocation of indiginous people, it's still not the same wood.
If you're lucky enough to find some recycled Burma Teak, then there's no reason not to use it. Good luck finding some.
The timber recycling industry is still in it's infancy, and there are millions of tons of high grade, high value timber lying around in old buildings. Here in Australia and also in NZ, tens of thousands of houses were floored with kauri in the 20's and 30's. To date I'm not aware of any company selecting the best of it for boatbuilding, but I expect someone will. At present you just have to buy lots and resell what you can't use.
I seem to recall reading about marine structures such as wharves, pilings, lock gates etc being built of first grade Burma teak. Some of those structures must still be standing, and will perhaps reappear as good timber one of these days - if they're not just bulldozed and burned.

[ 07-23-2003, 01:30 AM: Message edited by: Aramas ]

[Nicholas Carey]

Originally posted by Ken Hall:
Another question: In The Riddle of the Sands, yawl Dulcibella was a converted lifeboat built of double-diagonal teak.

I've been intrigued with that method and material ever since I read the book. D'you reckon that you'd have to steam the inner planking to force it to shape? I'm not familiar with the bending properties of teak, but I like everything else about it.Well...we had to steam Pirates new [outer] planks. Bear in mind, though, that with double-planking, the planks are half the thickness they would be otherwise.

The garboards, though, had to be installed very thick, and then carved to shape, due to the tight turn involved.

[On Vacation]

Like this Nick? ;) I would hate to figure the cost of planking a new boat the size of Pirate with teak with today's prices.
http://www.imagestation.com/picture/sraid18/pee4a75b05524c1135171f6bdb0fc9a17/fdd3693f.jpg

[RodB]

Repairing the double planking seems like it would be a real pain! Oysters comments on ( another posting) strip-planking by the powerboat builders raises one's opinion on sheath-stripped construction.

RB

[ 07-23-2003, 05:56 PM: Message edited by: RodB ]

[Nicholas Carey]

Hey! What am I doing in that picture :D

I'm not sure repairing the planking was any worse than normal single-planked carvel (removing the nails and old frames was the most labor-intensive,) but it is twice the spiling and twice the fasteners.

Gooping betwixt layers was, um, messy, though (we used white lead paste.)

[On Vacation]

I beleive discussing double planking in the year of Pirate and double planking with strip planking methods now, with the glues, can change the idea of repairs. ;) :D I guess "some" should go back and update the scenarios, or opinionated opinions, in one big post, which building in todays enviroment of the three methods, are, could, think, be for some people. But traditional planking methods in Miami waters, fulltime, not in my life time.

[ 07-24-2003, 08:10 AM: Message edited by: Oyster ]

[Ken Hall]

Beautiful! Thank you for the information, Nicholas and Aramas. BTW (Aramas), recycled wood is a bit hit-or-miss here in the States, but some entrpreneurs seem to be waking to the opportunity.

[Aramas]

I've read the book and seen the movie so many times!
Does anyone know anything about the boat used in the movie? It was a lot roomier than the Dulcibella of my imagination. It had the companionway half way along the starboard side of the deckhouse - a rather odd and unseaman-like 'feature' imo.
I gather that a lot of old lifeboats were double diagonal - even the beach-launched surf lifeboats of the day. I suppose that it was considered inconvenient to wait a day for carvel or lapstrake seams to take up when deployed smile.gif